The manufacturing of iron core punching is one of the important links in motor manufacturing. The workload of sheet metal stamping manufacturing is the largest, the technical requirements are the strictest, and the requirements for molds are also the highest, which is an important factor affecting economic benefits. Therefore, it is necessary to pay attention to the research of the core sheet metal stamping manufacturing process and related mold structure issues.
一、 Type of lamination
In order to facilitate the study of the structure and process of motor cores, they are divided into circular punching, fan-shaped punching, and magnetic pole punching according to their shape.
1. Circular punching plate
Figures 1-4 show the stator and rotor laminations of AC motors and the armature laminations of DC motors. The maximum width of the electrical steel plate is 1200mm. Considering the machining allowance during punching, the diameter of the round punching plate should be taken into account Φ≤ 1180mm.
Figure 1 Small asynchronous motor stator lamination
The stator lamination of a small asynchronous motor is shown in Figure 1, with dovetail grooves punched on its outer circle to facilitate the installation of buckles and fastening of laminations as a whole during iron core pressing.
Figure 2 shows the rotor lamination of a small asynchronous motor. The rotor punching shaft hole has a keyway (with its corner serving as a marking) and a balance groove. The balance groove is designed to reduce the imbalance of the rotor.
The above figure shows the stator lamination of the internal pressure structure of a medium-sized AC motor, which is a round lamination directly stacked inside the frame.
The above figure shows the armature lamination of a DC motor, with axial ventilation holes (this structure lamination is also available for AC motors). The groove of this type of armature punching piece does not have a small groove with a slot wedge, but there are two different diameter punching pieces in one iron core. The smaller diameter punching piece is set in a certain position, and after embedding the wire, non-magnetic steel wire or weft free glass ribbon is tied on the small diameter iron core section to tighten the gasket or winding group.
2. Fan shaped slice
When the core diameter of steam turbine generators, hydro generators, and other large and medium-sized motors exceeds 1180mm, fan-shaped punching plates are required. Considering material utilization and existing equipment conditions, some small motor stator cores also adopt a fan-shaped blade structure.
1) Stator sector punch
Although this type of lamination has a similar fan-shaped shape, it has multiple different appearance forms due to its different stacking methods. The two common types of stator sector punching are shown in Figure 5.
2) Rotating fan-shaped punching plate
When the diameter of the rotor core is greater than 1180mm, fan-shaped punching plates are used for assembly. Figure 6 shows the fan-shaped punching of even numbered slot rotors（ α Is the angle between adjacent slots, where z is the number of slots for each fan-shaped sheet. Figure 7 shows the odd slot rotor sector. Figure 8 shows three commonly used rotating armature sector plate structures.
3. Magnetic grade lamination
Magnetic grade laminations are generally made of thicker (1-2mm) A3 or 16Mn steel plates. Figure 9a is a type of main magnetic pole lamination for DC motors, b and c are rotating magnetic pole laminations, and d and e are eddy current brake magnetic pole laminations.
二、 Technical requirements for lamination
1. Dimensional accuracy
There are multiple sizes on the punching plate, which can be classified as "internal size" and "matching size". Internal dimensions such as slot size, ventilation holes, marking slots, and aperture size on magnetic pole laminations generally use H10. A higher accuracy level is not necessary because the error caused by lamination is much greater than the error caused by lamination itself. The selection of precision level for the fitting dimensions of inner and outer circles, as well as shaft holes, with other parts is related to the processing technology used.
The accuracy of the inner and outer diameter dimensions of stator laminations in small and medium-sized asynchronous motors is related to their installation method. Generally, the outer diameter of the stator punching plate is H8, and the accuracy of the outer diameter is related to the process plan to ensure the coaxiality of the stator.
1) In the "light outer circle" scheme, there is a machining allowance of 0.5mm for the outer diameter of the punched sheet, with an accuracy of H8 or H9.
2) The tolerance of the outer diameter of the punching plate in the "two not only" and "smooth stop" schemes is determined by the accuracy of the punching plate and iron core. Due to the fact that the outer diameter size tends to increase after the iron core is pressed. Therefore, the upper limit of the outer diameter tolerance of the punching plate is 0.035-0.045mm smaller than the corresponding upper limit of the outer diameter of the iron core (0.035mm for smaller diameters), and its lower limit is generally determined by the H7 tolerance. Table 1 lists the outer diameter tolerances of the stator laminations and iron cores of JO2 series externally pressurized small asynchronous motors.
The outer diameter of the internal pressure stator punching plate is generally H7, and the inner diameter is H8. Table 2 lists the inner diameter tolerances of the inner pressure stator core.
2. Punching burrs
1) The stator punching is generally controlled within 0.05mm. For individual parts of the duplex punch (with a length of about 30mm), it should be controlled within 0.12mm, but burrs should be removed and the processed area should be within 0.08mm.
2) The burrs on the rotor punching should be controlled within 0.07mm, and individual groove shaped parts are not allowed to exceed 0.10mm.
3) For the punched pieces after painting, the burrs shall not exceed 0.05mm.
3. Film warping during punching
After punching, the punched pieces will experience varying degrees of warping. The warping value of punched pieces made with a single slot is relatively large, especially for rotor punched pieces with closed slots. After punching with a single slot, the warping is severe. The outer diameter of punched pieces below 230mm is not allowed to exceed 2mm, and those above 230mm are not allowed to exceed 3mm.
1) When punching the inner circle or shaft hole with the outer circle, the coaxiality should generally be controlled within 0.04-0.06mm. When punching the inner and outer circles twice, the coaxiality should be appropriately relaxed.
2) The unevenness of the distribution of teeth in the punching groove (also known as the difference between the maximum and minimum tooth widths) should comply with the provisions of the drawings and relevant process documents. If there is no clear regulation, the accuracy inspection of level 3 or level 4 in Table 3 can be referred to.
Some factories stipulate that the difference between flowing teeth and fixed teeth should not exceed 0.12mm and 0.2mm, respectively.
3) The centerline of the groove should pass through the center of the circle and there should be no obvious deviation. During inspection, align the shaft holes (or outer diameter) of the front and back plates, and align one end of the groove root. The distance between the two teeth should not exceed 0.8mm.
4) The insulation layer on the surface of the film should be thin and uniform, with sufficient dielectric, oil resistance, moisture resistance, and adhesion properties
Motor New Vision 2024-01-04 17:49 Published in Shanghai